Magnetic devices such as inductors are often used in circuit design for electronic devices (e.g., power modules) in which energy is stored in a magnetic field surrounding an electrically conductive element such as a coil of copper wire. To produce an inductor that can store a useful amount of energy for a given size and a given current level, a number of electrically conductive turns or wires are formed around a magnetic structure or core such as a layer of magnetic material. The magnetic field is enhanced by the permeability of the magnetic material and by the presence of the multiple conductive turns. As the size of electronic devices has been reduced by using integrated circuits and printed wiring boards with surface mount assembly techniques, the size of inductors has not, to date, decreased proportionately.
Attempts to use finer wire sizes have resulted in inductor designs with limited current handling capability. Silver is recognized as a slightly better conductor than copper for higher current levels, but its expense is generally not warranted in practical products. These effects have combined to make the design of magnetic devices a continuing object for further size and cost reductions without compromising the respective current ratings.
A number of approaches beyond the use of finer copper wire have been used in the past to produce smaller inductors. For instance, U.S. Pat. No. 6,094,123 entitled “Low Profile Surface Mount Chip Inductor,” to Apurba Roy, issued Jul. 25, 2000 and U.S. Pat. No. 5,802,702 entitled “Method of Making a Device including a Metallized Magnetic Substrate,” to Fleming, et al., issued Sep. 8, 1998, which are incorporated herein by reference, disclose magnetic devices that form recesses in a bar of magnetic material for conductors and deposit conductive material in the recesses. Additionally, U.S. Pat. No. 5,574,420 entitled “Low Profile Surface Mounted Magnetic Devices and Components Therefor,” to Roy, et al., issued Nov. 12, 1996, which is incorporated by reference, discloses a magnetic device that forms conductive pathways in a body of magnetic material, adds windings by inserting staple-like conductive piece parts through apertures in the body, and solders the staples to a patterned printed wiring board placed below a ceramic magnetic bar to complete the winding structure. Each of the magnetic devices disclosed in the aforementioned references suffer from a current limitation therefor, which is an impractical design and manufacturing approach for a mass market. The aforementioned magnetic devices also provide inadequate heat dissipation capability or reduction in the size thereof.
Thus, the designs for the magnetic devices in the past are inadequate to produce a sufficiently miniaturized magnetic device with a substantial current rating for application in compact devices such as high density power converters embodied in power modules. The power converters often employ magnetic devices that can sustain currents exceeding one ampere and are operable at switching frequencies that exceed one megahertz. Additionally, the magnetic devices should exhibit very low electrical resistance at the switching frequency and should be more compact than presently achievable designs. The design of power converters is inadequately served by these aforementioned limitations of present magnetic devices. In addition, a magnetic device integrable with manufacturing processes of the commensurate end product such as a power module would provide substantial cost savings therefor.
Accordingly, what is needed in the art is a magnetic device, and related method of forming the same, that can meet the more stringent requirements of present applications such as compact, efficient and high density power modules, while being manufacturable at high volume and with lower cost than is achieved with the prior art.